Some known vehicles include a subframe made by casting and provided on a vehicle frame for supporting thereon a structural component such as a transmission. The subframe is formed into a hollow shape by means of a core which is disposed in a cavity of a casting mold when the subframe is formed by casting. The subframe further has a core discharge opening (hereinafter referred to as “sand discharge opening”) formed at a bottom part thereof for allowing the core to be discharged after casting. By virtue of the hollow shape, the subframe is made light in weight (See, Patent Document 1, for example).